1. Field of the Invention
The present invention relates to encoded remote electrical control systems, and particularly to secure ignition systems for motor vehicles.
2. Description of the Prior Art
In a conventional motor vehicle ignition system, a key operated lock is used to actuate the ignition switch. Closure of the switch connects battery power to essential ignition system components such as the ignition coil and the distributor. In the "start" position, battery power also is supplied to the engine's starter. The security of such an ignition system depends on the integrity of the lock, and the degree to which the mechanical installation can prevent tampering or "hot-wiring".
A major weakness in conventional ignition systems is that the wire carrying power from the battery to the ignition coil goes by way of the ignition switch. Direct shorting of the switch contacts is all that is required to start and run the engine. Alternatively, the battery can be directly hot-wired to the ignition system components under the hood. Security is poor.
In the past, the usual approach to improving security has been to enclose the critical interconnections and components in rigid housings. At least one automobile manufacturer locates the ignition coil on the fire wall between the engine and the dashboard, and provides a unitary armored cable from the ignition coil housing to the key switch assembly. Since power must be supplied to the ignition coil to start the engine, "hot-wiring" can only be accomplished by physically destroying the armored cable assembly. While this can be done with the appropriate tools, it is sufficiently difficult so as to discourage a would-be thief who is anxious to accomplish the job quickly.
The difficulty with this prior art approach is that the cost of such armored assemblies is high, and their use complicates normal maintenance. For example, in the system just described if a wire within the ignition coil should break, the entire armored cable assembly must be taken out to permit removal and disassembly of the ignition coil. Replacement ignition coils are only sold as a unit with the armored cable attached.
An object of the present invention is to provide a secure ignition system for a motor vehicle which does not depend on extensive mechanical armoring to prevent theft or "hot-wiring". Another object is to provide a secure ignition system which utilizes an electrical code transmission device, preferably an integrated circuit chip contained in the ignition switch assembly, to transmit an encoded signal to a receiver/decoder associated with the essential ignition system components. Receipt of this signal causes the receiver/decoder to effectuate a necessary electrical connection to the ignition system component, thereby enabling engine operation.
"Hot-wiring" at the ignition switch is prevented since shorting of the leads to the switch and transmitter assembly will not cause transmission of the necessary code, and hence will not result in engine ignition. By enclosing the receiver/decoder and the circuitry used to effectuate the necessary ignition system connection in a small tamperproof housing, "hot-wiring" at the ignition coil or distributor likewise is prevented. The inventive system may be used in conjunction with a pushbutton type electronic combination lock in place of a key-operated lock.